Ovens for cooking and baking food have been known and used for thousands of years. Basically, oven types can be categorized in four different forms. The simplest and probably the oldest cooking resulted when man put some vegetable or grain products on a hot rock next to a fire, and cooked them essentially by the heat transfer method of conduction. With a little more refinement, an enclosure surrounding the heating element entrapped the heated air giving rise to cooking by convective heat transfer. This was the prototype for the modern gas or electric oven. In the past century, radiant energy from infrared radiation sources has been used to heat and cook foodstuffs directly. Within the past few decades, microwave radiation has proved useful in allowing very short cooking times for many types of food.
There are subtle differences between cooking and baking. Cooking just requires the heating of the food. Baking of a product from a dough, such as bread, cake, crust, or pastry, requires not only heating of the product throughout but also a chemical reaction coupled with driving the water from the dough in a predetermined fashion to achieve the correct consistency of the final product and finally browning the outside. Following a recipe when baking is very important. An attempt to decrease the baking time in a conventional oven by increasing the temperature results in a damaged or destroyed product.
In general, there are problems when one wants to cook or bake foodstuffs with high-quality results in the shortest times. Conduction and convection provide the necessary quality, but both are inherently slow energy transfer methods. Long wave infrared radiation can provide faster heating rates, but it only heats the surface area of most foodstuffs, leaving the internal heat energy to be transferred by much slower conduction. Microwave radiation heats the foodstuff very quickly in depth, but during baking the loss of water near the surface stops the heating process before any satisfactory browning occurs. Consequently, microwave ovens cannot produce quality baked foodstuffs, such as bread.
Just as with baking, there are drawbacks with the conventional methods of popping corn. To pop "popcorn", the kernels must be heated so that internal heat buildup cause the kernel to explode. Once the kernel has exploded, it is desireable for the cooking process to stop.
One conventional method of popping corn is to heat the kernels on a hot surface. There are drawbacks to this method. First, heating surface affects a small volume of the kernels; the spot on the kernel that contacts the hot surface. Second, the "husk" (outer surface) of the kernel tends to burn on the spot that contacts the hot surface. Once the kernel has popped, the popped kernel, including the attached husk, continues to burn on the spot that contacts the hot surface because the popped kernels are not separated from the unpopped kernels. The burned spots give the popcorn an undesirable burn taste.
To help alleviate this problem, one may shake or constantly stir the popped and unpopped kernels. Additionally, the heated surface temperature may be reduced. And finally, the cooking process can be stopped before all the kernels are popped. The result is that there still is a burn taste, the process is slow, and not all the kernels are popped leaving waste kernels mixed in with the popped kernels.
Another conventional method to cook the kernels is to use hot oil. This tends to speed up the heat transfer to the kernel and provide a more uniform application of heat to the kernel. While this process addresses spot burning, cooking with oil has its disadvantages. Hot oil can still burn the popcorn if the oil is too hot or if the kernel takes too long to pop. Further, it leaves an undesirable residue on the popcorn that carries the burn taste from burned kernels to the popped corn. Finally, the popped kernels continue to cook after popping.
A third method of popping corn is by the use of an oven. Conventional ovens, however, can't transfer heat to the inside of the kernel fast enough to be speed efficient. And the problems of overcooking the popped corn and the presence of wasted unpopped kernels are still present.
Microwave popping corn addresses the most predominant problem of popping corn: speed. But still, the problems of spot burning, overcooking of the husk and popped corn, and leftover unpopped kernels are still present. Additionally, microwave popping of corn is hard to do in mass quantities, such as in movie theaters.
Hot air popping machines, which cook the kernels with swirling hot air, address the spot burning problem. The popped corn, however, still swirls in hot air after popping so overcooking is still a problem. And as always, the speed is never sufficient.
There is a need for a very fast method of cooking popping corn that does not spot burn, does not continue to cook the corn once it is popped, does not leave a residue on the popped corn, and does not leave leftover unpopped (waste) kernels intermixed with the popped corn.